The present invention relates to mold apparatus and more particularly to apparatus for facilitating removal and replacement of a single mold in a multi-mold rotational mold configuration which, in addition, facilitates opening of all molds simultaneously.
A molding cycle includes the steps of bringing together two or more mold parts to form a mold having a cavity in which an article may be cast, placing particulate material inside the mold, heating the mold until the material inside is melted, rotating the mold about several different axes so that the entire cavity surface is coated with the melted material and then allowing the mold to cool so that the melted material hardens and forms an article. Rotation about several axis is accomplished by securing the mold to a multi-articular machine which can facilitate the required movement.
Each step in a molding cycle requires a finite amount of time, the total cycle time referred to hereinafter as a cycle period. Process efficiency is generally measured by the number of articles which can be formed in a given period which is directly related to the duration of the cycle period.
To increase process efficiency, the industry has designed mold apparatus which can form several articles during a single cycle period. The most common multi-mold apparatus include several (e.g. 10) molds which are mounted to a "spider" wheel system which includes matching rigid spider wheels. Where each article mold consists of first and second mold halves, each first mold half is secured to a first spider wheel and each second mold half is secured to a second spider wheel. The spider wheels are constructed such that when the wheels are secured together, each second mold half is aligned with a corresponding first mold half forming a mold cavity and the molds are arrayed radially about a rotation axis.
With particulate material in each first mold half, the spider wheels are secured together forming separate yet mechanically linked molds. The spider wheel system is then secured to a multi-articulate machine and the heating, rotating and cooling steps described above are performed. To remove articles from the molds after cooling, the second spider wheel is moved axially away from the first spider wheel simultaneously opening all mold halves. U.S. pat. No. 5,306,564 describes a typical spider wheel system.
Typically spider wheels include rigid legs spaced around their perimeters which cooperate to separate adjacent wheels and form a space therebetween where molds are mounted. While the spacer legs are necessary, the legs limit the types of molds which can be used with a particular spider to a single mold family. In other words, spider wheels are custom built to accommodate specific types of molds.
Sometimes it is desirable to replace either all or a subset of molds which are linked to a multi-articulate machine so that articles having different characteristics can be formed. To replace all molds in a first set with molds in a second set which have different characteristics, one solution has been spider wheel refabrication. Unfortunately, refabrication is extremely time consuming and labor intensive and is therefore relatively costly and thus avoided.
Another solution for replacing mold sets has been to detach a first set of spider wheels and replace the wheels with a second set of wheels specifically designed to accommodate the second set of molds. While replacement requires less time and less labor than refabrication, the extreme complexity of wheel-machine coupling systems makes even the replacement solution relatively labor intensive and time consuming. This is particularly true because spider wheel replacement typically extends the molding cycle period.
The cycle period is extended because system hardware does not facilitate wheel replacement simultaneously with one of the previously mentioned process steps (e.g. heating, rotating, cooling). Generally, mold systems do not facilitate wheel replacement while mold cavities are formed. Instead, replacement is only possible when spider wheels are decoupled from the multi-articulate machine. During a process cycle, except for at the beginning of the cycle when particulate material is placed inside a mold half and at the end of the cycle when a product is removed from a mold, the mold halves must be secured together. Particulate provision and product removal require minimal time and, in any event, require much less time than is needed to decouple spider wheels from a multi-articulate machine and recouple different wheels to the machine to accomplish replacement. Thus, mold replacement necessarily extends a molding process cycle and reduces process efficiency.
To replace a subset of molds on a wheel system the only solution is refabrication which, as indicated above, is time consuming and labor intensive and therefore expensive.
There is, therefore, a need for a mold system which facilitates easy replacement of a mold in a spider wheel system. It would be particularly advantageous if molds could be replaced without separating mold halves and while the spider wheels are secured to an associated multi-articulate machine so that a mold could be removed from the wheels and replaced during a molding process cooling step thereby limiting the time between molding processes.